Chapter 5 & 6 Concept Checks

From the cross AB/ab ab/ab, what is the recombination frequency if the progeny numbers are 72 AB/ab, 68 ab/ab, 17 Ab/ab, and 21 aB/ab?

0.231

If a heterozygous parent (AB/ab) is test-crossed to a homozygous recessive (ab/ab), what will the progeny phenotypic ratio be if genes A and B are completely linked?

1AB:1ab

One species has 2n = 32 chromosomes and another species has 24 chromosomes. In an allotriploid of these two species, how many chromosomes would there be?

44 or 40

If genes A and B are linked, what is the maximum percentage of recombinant gametes that can be produced if a single crossover occurs during gametogenesis?

50%

A diploid species has a total of 52 chromosomes. How many chromosomes would be found in monosomy, trisomy, and in an autotriploid individual?

51, 53, and 78

In a three-point testcross the nonrecombinant progeny are A+ B+ C+ and a b c. The double-crossover progeny are A+ B+ c and a b C+. Which locus (A, B, or C) is in the middle?

C

Were the genes in the heterozygous parent coupled or in repulsion?

Coupled

For single crossovers, the frequency of recombinant gametes is half the frequency of crossing over because

Each crossover takes place between only two of the four chromatids of a homologous pair

Recombination rates are the same in all species and between males and females of species.

False

Aneuploids of which chromosomes are less likely to result in a live birth?

Larger autosomes

What is the outcome of a Robertsonian translocation?

One large metacentric chromosome and one very small chromosome with two very short arms

The following testcross produces the progeny shown: Aa Bb x aa bb --> 10 Aa Bb, 40 aa Bb, 40 aa Bb, and 10 aa bb. Were the genes in the Aa Bb parent in coupling or repulsion?

Repulsion

What is the most likely order of the linked genes R, S, and T if the distance between R and S is 22 m.u., the distance between S and T is 8 m.u., and the distance between R and T is 14 m.u.?

STR

A three-point testcross is used to determine the order of three linked genes. The following crossover classes occur: single crossovers, double crossovers, and no crossovers (nonrecombinant). When compared to the no-crossover progeny, what other crossover class needs to be considered in determining gene order?

The double-crossover class

In performing a dihybrid cross, you expect to see a 9:3:3:1 ratio. What is a good explanation if you do not see a 9:3:3:1 ratio in a dihybrid cross?

The two genes are linked.

You calculate an interference of 0.59. What does this number tell you?

You will not observe 59% of expected double crossovers.